But he soon started suggesting that the security services had been involved.

He said on Friday that he went to Ukraine on the understanding he would meet the last elected president of Chechnya, Aslan Maskhadov, for peace talks.

He said that, on arrival at an apartment in Kiev, he was offered some refreshments and suddenly became "very drowsy".

Mr Rybkin said he was unconscious for four days, coming to on 10 February.

As he awoke, he claims one of his guards told him it was part of a "special operation".

"Then they showed me a revolting videotape with my participation and they told me it was a plan to compromise me and force me to be co-operative."

Mr Rybkin told reporters: "After what happened in Kiev, I am convinced that this election is a game without rules and it can end for me without ever beginning.

"That is why I will continue my campaign from abroad and then we shall see. This will be an active and uncompromising struggle.

"As a registered candidate I have a chance to address the Russian people, even through those mass media that would normally censor even a hint of a view
that is critical of the ruling regime," he said.

Putin ahead

The BBC's Steve Rosenberg in Moscow says the afternoon bulletin on Russian state television made no mention of Mr Rybkin's sensational claims.

Instead, it showed President Vladimir Putin - who is expected to easily win the poll - busy running the country.